JERUSALEM — A bus racing to a prison to save mostly Palestinian inmates from an approaching forest fire burst into flames yesterday — killing at least 36 Israeli guards from other prisons who had volunteered for the rescue mission, officials said.

The blaze, which had already torched 800 acres, was still out of control last night.

“This is a disaster of unprecedented proportions,” said Prime Minister Benjamin Netanyahu, appealing to Cyprus, Greece, Italy and Russia for backup.

The FDNY and US Forest Service teamed up last night to ship a planeload of fire-retardant chemicals to help battle the fast-moving flames, Mayor Bloomberg said.

The fire, in the northern Carmel region, broke out around noon. Authorities evacuated hundreds of residents, then began moving the inmates out of Damun prison.